1,721,078 research outputs found
TEM characterisation of near surface deformation resulting from lubricated sliding wear of aluminium alloy and composites
Full text linkAluminium alloy composites have been extensively investigated for use in tribo-contact applications, however little detailed literature exists on the sub-surface microstructural evolution as a result of lubricated sliding wear. In this study two un-reinforced alloys (2124 and 5056) and identical alloy composites, reinforced with 15 vol.% MoSi2 intermetallic particles were produced by a powder metallurgy route and subject to lubricated sliding at initial Hertzian contact pressures of 0.9–1.2 GPa. Focused ion beam (FIB) techniques were used to produce thin sections parallel to the worn surface. Sub-surfaces layers were then examined in detail by transmission electron microscopy (TEM). Results indicated that the depth of deformation was minimal in the alloys, with the most highly deformed polycrystalline layer confined to approximately 1 ?m below the worn surface. Equiaxed sub-grain sizes of around 0.1 ?m were comparable to that observed for dry sliding of similar alloys and composites [1]. Evidence of surface erosion by solid particle impact was also observed, with wear debris generated as a result of material exceeding the ductility limit. For the composites, the MoSi2 provided a suitable means of transferring the normal contact load from asperity contacts to areas in the bulk of the sample. Reinforcement fracture was observed both at the worn surface and in areas further away in the bulk, for particles which were in direct contact with each other. Evidence of the deformation of the aluminium matrix below reinforcements was also present, with average sub-grain sizes of around 330 nm. Thus, such intermetallic reinforcements may have potential to replace reinforcements that are more abrasive to counterfaces, such as SiC or Al2O3, whilst still providing adequate wear resistance for the aluminium alloy.<br/
Lubricated sliding wear behaviour of aluminium alloy composites
No full textInterest in aluminium alloy (Al-alloy) composites as wear resistant materials continues to grow. However, the use of the popular Al-alloy-SiC composite can be limited by the abrasive nature of the SiC, leading to increased counterface wear rates. This study reports new Al-alloy composites that offer high wear resistance, to a level similar to Al-alloy-SiC. Aluminium alloy (2124, 5056) matrix composites reinforced by nominally 15 vol.% of Cr3Si, MoSi2, Ni3Al and SiC particles were prepared by a powder metallurgy route. The aluminium alloy matrix was produced by gas atomisation, and the Cr3Si, MoSi2 and Ni3Al were prepared by self-propagating high temperature synthesis (SHS), while the SiC was from a standard commercial supply. Following blending, the particulates were consolidated by extrusion, producing a homogenous distribution of the reinforcement in the matrix. Wear testing was undertaken using a pin-on-ring configuration against an M2 steel counterface, with a commercial synthetic oil lubricant, at 0.94 m/s and a normal load of 630 N, corresponding to initial Hertzian contact pressures of 750–890 MPa (the exact value depending on the material properties). Specific wear rates at sliding distances exceeding 400 km were in the range 4.5–12.7 × 10?10 mm3/Nm. The monolithic alloys gave the highest specific wear rates, while the MoSi2 and Cr3Si reinforced alloys exhibited the lowest. The worn surface has been analysed in detail using focused ion beam (FIB) microscopy to determine the sub-surface structural evolution and by tomographic reconstruction of tilted scanning electron microscopy (SEM) images, to determine the local worn surface topography. Consequently, the wear mechanisms as a function of alloy composition and reinforcement type are discussed.<br/
Characterisation of the oxide film on the taper interface from retrieved large diameter metal on polymer modular total hip replacements
No full textMany metal joint failures have been associated with adverse local tissue reactions due to the response of the body to wear debris and corrosion products, released from the bearing surfaces or the taper interfaces. It is believed that the oxide film on the CoCrMo alloy is playing an important role on the corrosion resistance, however, there is a lack of quantitative data on this aspect. In the present study, detailed analysis of the surface layer on the taper interfaces is provided using advanced electron microscopies. Two retrieved taper interfaces were analysed. The taper interface varies along the length of the tapers. Site-specific FIB/TEM cross-sections from different regions all show evidence of the oxide film and the carbonaceous layer, separately or mixed. HRTEM results showed the oxide film had porous texture and EELS confirmed the film was chromium oxide
Site specific SEM/FIB/TEM for analysis of lubricated sliding wear of aluminium alloy composites
No full textAlthough extensive research has been undertaken into the dry sliding wear of aluminium alloys, only limited work has been reported on lubricated wear. In this paper, the lubricated sliding wear of some powder derived aluminium alloy composites is reported. Stereo pairs of the worn surface were obtained in the SEM and digitally reconstructed to give an accurate projection of the surface topography. Analysis of the average surface roughness (Ra) along chosen sections provided quantitative information about the wear mechanism. Following this, dual beam focused ion beam (FIB) was undertaken to further explore the features revealed by the SEM surface reconstructions, with TEM sections removed from selected regions. Surface deformation was confined to a narrow layer, typically 1µm thick. Subgrain size within the subsurface layer was comparable to that found in dry sliding wear tests. Reinforcement fracture occurred in the surface particles only. The resultant fragments were often incorporated back into the surface following detachment, such that the total volume fraction reinforcement at the surface was greater than in the bulk. Thus, the dynamic surface topography was a result of three factors: surface deformation, local detachment of reinforcement and re-incorporation of the fragments back into the surface.<br/
Dry sliding wear behaviour of powder metallurgy Al-Mg-Si alloy-MoSi2 composites and the relationship with the microstructure
Full text linkThe effect of the microstructure on the dry sliding wear of six aluminium alloy 6061 matrix composites reinforced with 15 vol.% of MoSi2 particles and two monolithic 6061 alloys processed by powder metallurgy with and without ball milling has been studied. Wear testing was undertaken using pin-on-ring configuration against an M2 steel counterface at 0.94 m/s and normal load of 42, 91 and 140 N. The wear resistance of the aluminium alloys was significantly improved by ball milling and the addition of reinforcing MoSi2 particles due to a more stable and more homogeneous microstructure, which avoids the detachment of the mechanically mixed layer. Wear rate of materials in T6 decreases as solutionized hardness of the materials increases. This behaviour is rationalized by taking into account the precipitation state of the matrix. In addition, wear rate follows a Hall–Petch type relationship, showing that the reduction of matrix grain size plays an important role in the increase in the wear resistance of the composites. The results indicate that the present intermetallic reinforced composites can be considered potential substitutes for ceramic reinforced aluminium alloys in tribological applications
Subsurface modifications in powder metallurgy aluminium alloy composites reinforced with intermetallic MoSi2 particles under dry sliding wear
Full text linkThe effect of dry sliding wear on the subsurface of six AA6061/MoSi2/15p composites processed by powder metallurgy with varying mixing methods (wet blending, rotating cube and ball milling) and reinforcement sizes was investigated. Three regions could be distinguished: the tribolayer or mechanically mixed layer (MML), the elasto-plastically deformed layer, where deflection of material occurs, and the unaffected bulk. The MML was not uniform along the surface and no relation could be found between the size/shape of MML areas and processing variables or applied loads. In the second region, particles close to the MML were found to be fragmented only in the composites processed using low energy. These composites were the only ones to show hardening, together with the similarly processed unreinforced alloy. It can be concluded that, although the subsurface of these composites are noticeably affected by dry wearing through formation of a mechanically mixed layer and material deflection, the ball milled composites do not suffer subsurface hardening and their reinforcing particles do not break during the test. It is also evident from the present research that no simple correlation exists between the size/shape of the tribolayer and deflection parameters and processing variables or applied loads
Microabrasion-corrosion of cast CoCrMo alloy in simulated body fluids
No full textWear and corrosion of metal-on-metal hip replacements results in wear debris and metal-ion release in vivo, which may subsequently cause pain and hypersensitivity for patients. Retrieved metal-on-metal hip replacements have revealed that two-body sliding wear and three-body abrasive wear are the predominant wear mechanisms. However, there is a lack of understanding of the combined effects of wear/corrosion, especially the effect of abrasion–corrosion.This study investigates the sliding–corrosion and abrasion–corrosion performance of a cast CoCrMo alloy in simulated hip joint environments using a microabrasion rig integrated with an electrochemical cell. Tests have been conducted in 0.9% NaCl, phosphate buffered saline solution, 25% and 50% bovine serum solutions with 0 or 1 g cm–3 SiC at 37 °C. Experimental results reveal that under abrasion–corrosion test conditions, the presence of proteins increased the total specific wear rate. Conversely, electrochemical noise measurements indicated that the average anodic current levels were appreciably lower for the proteinaceous solutions when compared with the inorganic solutions. A severely deformed nanocrystalline layer was identified immediately below the worn surface for both proteinaceous and inorganic solutions. The layer is formed by a recrystallisation process and/or a strain-induced phase transformation that occurs during microabrasion–corrosion
Predicting microstructure and strength of maraging steels: Elemental optimisation
Full text linkA physics–based modelling framework to describe microstructure and mechanical properties in maraging steels is presented. It is based on prescribing the hierarchical structure of the martensitic matrix, including dislocation density, and lath and high–angle grain boundary spacing. The evolution of lath–shaped reverted austenite is described using grain–boundary diffusion laws within a lath unit. The dislocation density provides the preferential nucleation sites for precipitation, whereas descriptions for particle nucleation, growth and coarsening evolution are identified for Ni3Ti, NiAl and its variants, and BCC–Cu clusters. These results are combined to describe the hardness at different ageing temperatures in several [Formula presented], [Formula presented] and [Formula presented] steels. A critical assessment on individual contributions of typical alloying elements is performed. Ni and Mn control the kinetics of austenite formation, where the latter shows stronger influence on the growth kinetics. Ti additions induce higher hardness by precipitating stronger Ni3Ti, whereas Cu clusters induce low strength. A relationship between the reverted austenite and the total elongation in overaging conditions is also found. This result allows to identify optimal process and alloy design scenarios to improve the ductility whilst preserving high hardness in commercial maraging steels
High temperature tribological performance of CrAlYN/CrN nanoscale multilayer coatings deposited on ?-TiAl
No full textThis paper details the effect of temperature on the frictional behaviour of highly novel CrAlYN/CrN multilayer coatings, deposited by High Power Impulse Magnetron Sputtering (HIPIMS) on a Titanium Aluminide alloy used as fan blade material in the aerospace and a turbo-charger wheel in the automotive industries. The work was the first to discover the high temperature oxide 'glaze' layer formation which occurred on CrN multilayer-type coatings at higher temperatures and has received significant attention in the literature because of this finding.<br/
Sub-surface characterisation of tribological contact zone of metal hip prostheses
No full textMany metal on metal joint failures have been associated with adverse local tissuereactions due to the response of the body to wear debris and corrosion products, released from the bearing surface or the taper interface. Both a carbonaceous layer and an oxide film are reported on the CoCrMo metal joints, which play important roles in the wear resistance of the material. However, there is a lack of quantitative data on the structure and distribution of the carbonaceous layer and the oxide film. The current work provides a detailed investigation of the surface damage on retrieved CoCrMo taper interfaces. In addition, systematic differences in the starting surface structure of biomedical CoCrMo were studied through a comparison of a standard mechanical polished (MP) and an electropolished (EP) surface after reciprocating test. Site-specific FIB/TEM cross-sections show the evidence of the carbonaceous layer and the oxide film on both CoCrMo taper interfaces and MP, EP CoCrMo, ranging from 5 -500 nm depending on the location. The amorphous carbonaceous layer exhibits a π * peak in the EEL spectra, with trace of Ca and N. The oxide film on the taper interfaces has a porous texture and HRTEM indicates chromium oxide nano-crystals in an amorphous background, however, only a very thin oxide film (~ 2 nm) exists on MP and EP CoCrMo after reciprocating test
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